1. Field of the Invention
The present invention relates to an electrode plate for use in an alkaline storage battery and an alkaline storage battery using the same.
2. Description of the Related Art
Recently, as information apparatuses, such as cellular phones, PHS (Personal Handyphone System) phones, and notebook computers, are coming into wide use, a high value-added, compact and lightweight secondary battery having high energy density has been newly developed. Further, another secondary battery having high energy density has been newly developed as a power source of an electric car. Under such circumstances, there is need in the marketplace for batteries which are more compact and have higher capacity.
Particularly, in an alkaline storage battery, there is a problem of how to increase a filling density of conductive paste in a limited volume.
In general, a negative electrode plate, which includes a core material coated with an active material, is used in an alkaline battery. As shown in FIG. 7, punching metal, which is a nickel-plated steel sheet including a plurality of round through-holes 22a filled with an active material, is used for the core material of the negative electrode plate. The through-holes 22a are arranged across a core material 22 along longitudinal and width directions thereof so as to form a staggered pattern. In the alkaline storage battery, the negative electrode plate using such a core material 22 and a positive electrode plate are laminated with a separator being sandwiched therebetween, and are spirally rolled. The rolled plates are concentrically placed in a cylindrical case. The cylindrical case is filled with an electrolyte of potassium hydroxide or the like.
In the case of a nickel-cadmium storage battery, the negative electrode plate includes a core material coated with conductive paste mainly containing cadmium. In the case of a nickel-metal hydride storage battery, the negative electrode plate includes a core material coated with conductive paste mainly containing a hydrogen absorbing alloy.
Generally, in order to increase a filling density of the conductive paste in the limited volume available, the negative electrode of the alkaline storage battery is pressed with high pressure after having been coated with the conductive paste or the proportion of the core material in the negative electrode plate is reduced by increasing an aperture ratio in the core material, i.e., a ratio of a total area of through-holes to an area of the core material.
However, excessive pressing increases warping in the electrode plate, deteriorating the processability. Further, an excessive increase in the aperture ratio in the core material reduces the strength of the electrode plate and core material portions through which electrons flow, causing an increase in electrical resistance.